The long-term aim of this project is a better understanding of mechanisms that underlie the ability to detect and recognize signals in complex spectro-temporal auditory backgrounds in normal and impaired hearing. The proposed work encompasses three specific aims investigating spectro-temporal processing in normal and impaired ears. The first specific aim is to obtain a better understanding of the effect of hearing loss on spectro-temporal processes that underlie our ability to "piece together" fragments of acoustical signals that are available when the S/N ratio is very poor. Here, we will explore the effects of sensori-neural hearing loss on 1) the ability to combine asynchronous spectro-temporal information in the perception of speech and pitch; 2) the ability to combine synchronous spectro-temporal information in the perception of across frequency speech cues; and 3) the facilitative effect of background noise when integrating fragments of spectro-temporal information (the induction effect). The second and third aims continue our established research program investigating the importance of across-frequency comodulation in normal spectro-temporal analysis. The second aim is to test between across-channel versus within channel accounts of comodulation masking release (CMR). The third aim is to test between across-channel versus within channel accounts of comodulation detection differences (CDD). Whereas the original interpretations of both CMR and CDD were based upon the analysis of across-channel information, recent research has challenged such interpretations, and has suggested that the phenomena may be accounted for by appealing only to peripheral, single-channel mechanisms. Psychoacoustical approaches involving temporal fringe manipulations, dichotic stimulus presentation, and informational masking are developed to test between these possible explanations. [unreadable] [unreadable]